A conventional gripper will be described below with reference to FIG. 10 as disclosed in the International Publication Number WO00/45999. In FIG. 10, the gripper 1 has a gripping finger 10 for gripping or releasing a minute object and having three V-character pieces 10v of substantial V shape, a conversion portion 20 for converting the rotation of a motor shaft 12a of a motor 12 into translation motion, the conversion portion 20 being connected to a shared portion 10g of the gripping finger 10, a connection portion 30 for connecting the conversion portion 20 and the shared portion 10g of the gripping finger 10, a case portion 40 for accommodating the motor 12, the conversion portion 20 and the connection portion 30, and a fixing portion 50 for fixing a fixing pawl 10t of the gripping finger 10 to the case portion 40.
The conversion portion 20 comprises a screw axis 22 for fitting and securing the motor shaft 12a of the motor 12 and having a male screw 22a around the outer circumference thereof, and a nut 26 for inserting the screw axis 22 and having a hollow portion formed with a female screw 26a to be mated with the male screw 22a, in which the rotation of the motor shaft 12a of the motor 12 is converted into translation motion of the nut 26.
The connection portion 30 is formed with a protruding portion 26c having a tapped hole centrally at the top end of the nut 26, in which the shared portion 10g of the gripping finger 10 is secured into this tapped hole by a screw 32.
The case portion 40 is formed of a cylindrical case 41 for receiving the motor 12 and a part of the screw axis 22, a lid 43 for closing a right end face of the case 41, and a holder member 45 engaged with a left end face of the case 41, in which the holder member 45 is like a barrel having a through hole, with a substantially trapezoidal shape in cross section, and has a female screw 45b on the outer face of a hollow portion 45a at the top end.
The fixing portion 50 is formed with a male screw for mating with the female screw 45b of the holder member 45 on an external circumferential face of a cylindrical presser ring 53. The fixing pawl 10t of the gripping finger 10 abuts onto the hollow portion 45a of the holder member 45, and the fixing portion 50 is securely pressed by the presser ring 53.
Referring to FIG. 10, the operation of the gripper as constituted above will be described below. First of all, the motor 12 is powered on, and then the motor shaft 12a of the motor 12 is rotated, so that this rotation is transmitted via the screw axis 22 to the nut 26 to move the nut 26 in a right direction as indicated in FIG. 10.
Along with this, the shared portion 10g of the gripping finger 10 is forcibly displaced by the same amount of displacement in the same direction, and the gripping finger 10 is subjected to a bending moment, so that the V-character pieces are bent at the top end portion in the direction coming closer to each other and closed to grip an object.
On the contrary, if the rotation of the motor 12 is reversed, with this rotation, the nut 26 is translated via the screw axis 22 in a reverse direction, and the shared portion 10g of the gripping finger 10 is also translated by the same amount of displacement in the consistent manner, so that the top end portions of the gripping finger 10 release the object.
However, if the gripping object of the gripping finger 10 is spherical, the gripping finger 10 maybe composed of three fingers as above described, but if the object is like a square pole, the gripping finger must be composed of two fingers (not shown) to grip the object appropriately. Also, the gripping finger 10 must be exchanged due to expiration of life, if a predetermined number of operation times is exceeded.
Such an exchange is perform in such a way that the screw 32 is firstly turned by a screwdriver (not shown) to release engagement of the protruding portion 26c of the nut 26 into the tapped hole, and then the presser ring 53 is turned by a spanner (not shown) to unscrew the holder member 45 from the female screw 45b, thereby detaching the gripping finger 10.
In order to attach the gripping finger 10 on the holder member 45, the screw 32 is tightened into the tapped hole of the protruding portion 26c by the screwdriver, the presser ring 53 is turned by the spanner and mated with the female screw 45b of the holder member 45. Thus, there was a problem that the exchange operation of the gripping member 10 was troublesome.
In addition, in the case where the gripper 1 is employed for an end effector of a robot, and particularly is attached vertically downward at the top end portion of a scalar robot to be actuated horizontally, the gripper 1 can not be disposed sideways or upward, resulting in a problem that the exchange operation of the gripping finger 10 alone was troublesome.
This invention is aimed at providing a gripper and its manufacturing method in which a gripping member is easily attached.